The technology disclosed herein generally relates to optical networks that enable communication between electrical components.
Data transmission between electrical components is typically achieved via a network comprising electrical cables. In analog avionic systems the number of cables used to transfer information between the various system components can be considerable. In digital systems, signals are transmitted along a single pair of wires, which makes up a data bus. A bus is a collection of wires through which data is transmitted from one part of a network to another. Bus systems provide an efficient means of exchanging data between the diverse avionic systems onboard an aircraft. All buses consist of an address bus and a data bus. Typically aircraft bus systems use serial data transfer because it minimizes the size and weight of aircraft cabling.
In some scenarios, it is desirable to connect a number of line replaceable units (LRUs) to each other. For example, a number of LRUs in the forward section of a vehicle (e.g., an aircraft) may be connected to a number of LRUs in the aft section of the vehicle. Connecting each LRU to every other LRU could result in an unreasonably large number of connections between LRUs. If all of these connections are in the form of copper wires, the resulting space and weight of the connections could be burdensome for the vehicle. Electrical data buses have been used to connect LRUs.
More specifically, it is known to use an electrical controller area network (CAN) to connect electrical devices (also known as “CAN nodes”) to each other by way of a multi-master serial bus (also known as a “CAN bus”). The devices that are connected by a CAN bus are typically sensors, actuators, and other control devices. For example, it is known to facilitate communication between a multiplicity of LRUs using an electrical controller area network.
Current electrical CAN bus assemblies on an airplane have many undesirable characteristics, including at least the following: (1) time-consuming assembly of T-couplers involving lifting and reconnecting the double shields on a cable; (2) critical stub lengths from the T-coupler to the LRU prevent reuse of a bus assembly for another CAN bus with the same node quantity; (3) CAN simple electrical signaling is not well protected from electro-magnetic effects (EME) as compared to Arinc 629 doublets; (4) careful treatment of terminator/T-coupler and T-coupler/node interfaces is required to avoid impedance mismatch; and (5) CAN operational issues. such as beyond economic repair, impedance mismatch, and bus reflection become worse for longer airplanes.
A single optical data bus can eliminate some of the weight and size of electrical connections between LRUs. In general, optical communication fibers, such as glass optical fibers and plastic optical fibers, can be lighter and contained in smaller spaces than electrical wiring. In particular, optical networking using plastic optical fibers may provide advantages over networking using copper or other metal wiring. Categories of plastic optical fiber include plastic-clad silicon optical fiber, single-core plastic optical fiber, or multi-core plastic optical fiber. Plastic optical fiber networking may have lower installation and maintenance costs. Moreover, because plastic optical fibers are lighter than the metal wiring that would be needed to carry an equivalent amount of data, using plastic optical fibers may result in appreciable weight savings. The weight savings may be significant for networks onboard vehicles, such as aircraft, where the weight savings may result in reduced fuel consumption and lower emissions.
At present, no industry standard is defined for the fiber optic transmissions of CAN signals. There are industry publication, patents and products for optical CAN bus but they use one or more of the following: separate fibers for transmit and receive to maintain separation of dominant bits and recessive bits; an active optical star with single point failure of the hub; and a single-fiber bidirectional flow of data from point to point (two-node bus) repeater for length extension with a dichroic mirror and two wavelengths.
It would be desirable to provide improvement to enhance the performance of CAN buses comprising a fiber optical network.